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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script src="js/jquery-3.6.0.min.js"></script>

    <script>

        let data = {
            'username' : 'wiken123',
        }
        $.ajax({
            data:JSON.stringify(data),
            url: 'http://localhost/check_username.php',
            type: 'POST',
            success:function(res){
                console.log(res)
            }
            
        })
    </script>
</body>

</html>